1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium and a method for producing the reversible thermosensitive recording medium.
2. Description of the Related Art
IC cards have been increasingly used in various aspects from users' daily lives to business activities. Actually, they are used as various cards (e.g., cash cards, credit cards, prepaid cards and ETC cards (electronic toll collection system)); in transportation facilities (e.g., railways and buses); as affiliate cards for digital broadcasting, 3rd generation mobile phones, etc.; in library service counters; and as student ID cards, employee ID cards, basic resident register cards, etc. Meanwhile, the amount of IC cards disposed of has been being increasing in accordance with diversification of the current economic and social activities.
In view of this, there is a keen need to create a recycling society, where material consumption is reduced and less environmental load is given, by reconsidering the current economic societies and lifestyles involving mass production, mass consumption and mass disposal to promote effective utilization and recycling of materials.
As one promising measure, electronic information recording module-embedded reversible thermosensitive recording media, wherein the electronic information recording module includes an electronic information recording element (hereinafter may be referred to as an “IC chip”) and an antenna circuit, can be used for reducing the amount of products disposed of. This is because they can rewrite information stored in the IC chip, show information as a visible image on their surface, and be used repeatedly.
Such electronic information recording module-embedded reversible thermosensitive recording media have been used in the manufacturing industry as instruction sheets such as operation sheets, parts management sheets and process management sheets. Actually, there is repeatedly performed a cycle including winding an instruction sheet around a rod-like part or inserting it into a card case, and rewriting the content of the instruction sheet.
When an image is formed on or erased from it, a heating device (e.g., thermal head, erase bar, erase roller and erase plate) of the printer is pressed against the instruction sheet. Thus, rewriting of a print image on the instruction sheet (reversible thermosensitive recording medium) must be performed so as not to break the electronic information recording module. Furthermore, desirably, the instruction sheet is flexible and shows a high-quality image.
Moreover, a tag may be bent when the tag placed on a table surface is picked up, and a tag is taken out from a holder. Thus, an IC chip portion in the tag is demanded to have mechanical durability against bending. Additionally, a medium is made flexible so as to improve efficiency of operation, such as picking up the medium.
Furthermore, from the viewpoint of improvement of close-contact properties with a thermal head so as to obtain high quality image, it is important to make a medium flexible.
If the surface of the reversible thermosensitive recording medium has concavo-convex portions and unevenness, a thermal head insufficiently comes into contact with a surface of the reversible thermosensitive recording medium and thus, heat is not sufficiently conducted in the surface thereof due to the heat insulating effect of air. As a result, the reversible thermosensitive recording medium cannot be rapidly cooled, causing failure in color development (unprinted image portion etc.) and a desired color development cannot be obtained in a part which is hard to be rapidly cooled.
Moreover, the thicker reversible thermosensitive recording medium adversely affects flexibility and reduces the number of reversible thermosensitive recording media which can be stacked in a stacker of a printer.
To solve there problems, proposed is a reversible thermosensitive recording medium (rewritable recording medium) including integrated component of a rewritable sheet having a reversible thermosensitive recording layer, and an electronic information recording module having an IC chip and an antenna circuit, wherein a core sheet having an opening mated with the IC chip is bonded using an adhesive between the rewritable sheet and the electronic information recording module (see Japanese Patent Application Laid-Open (JP-A) No. 2009-173013).
However, as sheets for compensating for the unevenness of the electronic information recording element is provided inside of the medium, the reversible thermosensitive recording medium becomes thicker, adversely affecting flexibility and reducing the number of reversible thermosensitive recording media which can be stacked in a stacker of a printer.
As a proposal for reducing the thickness of the reversible thermosensitive recording medium, a reversible thermosensitive recording medium is proposed that includes a module for an IC card having a substrate and an IC chip mounted on the substrate, wherein a concave portion is formed on a surface of a protective member for covering the IC chip, and a gap is formed between the protective member and the IC chip to prevent the protective member from directly contacting with the IC chip (see JP-A No. 11-11060).
However, the concave portion is required to be relatively deep in an attempt to reduce the thickness of the reversible thermosensitive recording medium. The deep concave portion results in large unevenness between the surface of the protective member and the bottom surface of the concave portion. Consequently, a resin is less likely to fill the concave portion completely and bubbles may be left when the resin is applied using an applicator onto the surface of the protective member on which the concave portion has been formed.
The problems are further described below in detail with reference to FIGS. 1A to 1D.
FIGS. 1A to 1D are each schematic view showing a step of applying a resin using an applicator onto a surface of a protective member in which a concave portion has been formed. Firstly, a first sheet-shaped base 3 provided on a reversible thermosensitive recording layer 1 is prepared, and a concave portion 2 having no tapered surface is formed by, for example, cutting out a surface of the first sheet-shaped base 3 opposite to a surface on which the reversible thermosensitive recording layer 1 is provided (see FIG. 1A). Next, a coating liquid for a first resin layer 11 is applied using, for example, an applicator 20 on the concave portion 2 and a surface of the first sheet-shaped base 3 in which the concave portion 2 has been formed (see FIG. 1B). The concave portion 2 having large depth prevents the resin from entering into a left corner of a bottom surface of the concave portion 2 when the applicator 20 passes through a left end of the concave portion 2, causing a gap “a1” to be formed. Similarly, when the applicator 20 approaches a right end of the concave portion 2, a gap “a2” may be left at a right corner of the bottom surface of the concave portion 2 (see FIGS. 1C and 1D).
When the resin in the concave portion 2 is cured and shrunk, a lack of the resin in the gap may deform a portion of the base 3 just under the gap, depressing the surface of the reversible thermosensitive recording layer 1.
Depending on the type of the resin used, the resin may react with residual air within the gap and moisture in the residual air to generate gas within the gap “a1” or “a2”, the resulting gas may form concave portions in the reversible thermosensitive recording layer 1.
Such concavo-convex shape of the surface of the reversible thermosensitive recording layer 1 results in white voids and failure in color development upon image formation using a thermal head.